This invention relates to a load limiting device for dissipating impact loads, and more particularly to a spool assembly which is used as a load limiting member in a structure to control its response to applied loads.
Controllable absorption of kinetic energy is desirable in many situations for reducing the impact of sudden stops, thereby keeping the level of transmitted loads within the limits of human tolerance. In a typical airplane or automobile crash, for instance, the vehicle experiences energy impulses which, if transmitted to the passenger, are capable of causing severe bodily injury or death. It has been shown that the largest number of injuries and facilities in such crashes occur when the seat fails to hold the passenger in place because of its inability to withstand the peak forces to which it is subjected. It is therefore desirable to equip these vehicles with seat structures which can absorb the energy of impact and thereby control the level of loads transmitted to the seat occupant.
In meeting this challenge, designers have developed seats which utilize load limiting devices such as wire bending apparatus, shock absorbers and inverting tubes to dissipate impact loads. Many of these devices, however, deform elastically when subjected to high impact loads, thereby resulting in recoil and subsequent human injury once the load is removed. Therefore, although the device may have successfully prevented a severe initial impact shock in one direction, it will not restrain relative motion in the opposite directions. In addition, those devices which are designed to deform plastically usually experience a high peak in the elastic region before plasticity is achieved or break upon application of severe loads. It is therefore desirable to design a device with a progressive load response, thereby protecting the seat occupant from any sudden movement which may cause injury.
Accordingly, it is an object of this invention to provide a device which is used as a load limiting member in a structure to control its response to applied loads.
Another object of the invention is to provide a device which will deform plastically at a prescribed load, thereby absorbing the kinetic energy of impact at a substantially constant rate throughout its deformation.
Yet another object of this invention is to provide a device whose response to loads can be controlled in a predictable manner.
Still another object of this invention is to provide a load limiting device which is lightweight, readily adaptable to present and anticipated vehicle construction techniques, easy to manufacture, and relatively inexpensive.